In a diesel engine, a fuel injection valve is usually arranged at a cylinder head and on an extension of an axis of a cylinder. An example of such conventional diesel engine is shown in FIGS. 1 and 2. In the figures, reference numeral 1 denotes a diesel engine which comprises a cylinder 2, a piston 3 slidably arranged in the cylinder 2 for vertically reciprocal movements, a fuel injection valve 5 mounted on a cylinder head 4, and openable and closable suction and exhaust valves (not shown) mounted on the cylinder head 4, a portion of the cylinder chamber above the piston 3 providing a combustion chamber 6.
The fuel injection valve 5 has a lower end formed with 4-6 nozzle holes which are arranged circumferentially and substantially equidistantly. An axis L1 of the fuel injection valve 5 is substantially on an extension of an axis L2 of the cylinder 3.
In the above-mentioned diesel engine 1, when the piston 3 reaches a vicinity of an upper dead center during a compression stroke, fuel is injected from the fuel injection valve 5 radially in a plan view into atomization in a combustion chamber 6 to produce sprays 7. To inject the fuel radially in the plan view is for prevention of the produced sprays 7 from being interfered with each other into formation of excessively rich portions of the sprays 7 and thus for prevention of combustion failure.
The sprays 7 radially injected into the combustion chamber 6 take in air supplied from the suction valve into the cylinder 2 and advance to and strike against an inner periphery of the cylinder 2, so that the sprays 7 change their advancing directions to advance along the inner periphery of the cylinder 2 and collide with the sprays 7 from the opposite direction along the inner periphery of the cylinder 2 into a fuel-air mixture which burns by attaining its ignition temperature through compression of the combustion chamber 6.
There are various prior art literatures for a diesel engine. A diesel engine with an axis of a fuel injection valve being on an extension of an axis of a piston is shown, for example, in Patent Literatures 1 and 2.    [Patent Literature 1] JP 2003-172144A    [Patent Literature 2] JP 10-227218A